1. Technical Field
The present invention relates generally to the strength measurement of composite materials. More particularly, the invention relates to a non-destructive method and system for measuring a minimum strength of a test specimen that involves bulk heating the test specimen at a localized region.
2. Discussion
In the aircraft design industry, a number of complex parameters such as aerodynamics, weight, and structural load resistance must all be considered and delicately balanced with various cost considerations. Structural load resistance (or strength) can be a particularly difficult parameter to work with at the design phase. For example, a typical aircraft will have hundreds of bonded composite materials, each having distinct strength requirements based on the anticipated load to be applied to the aircraft at the given location.
Conventional strength measurement approaches involve proof testing an entire structure, where the entire structure includes several substructures of interest. For example, the structure might be an entire aircraft wing made up of various stringers and ribs bonded to an outer skin. Although the substructure of interest may be only the outboard leading edge of the wing, conventional proof testing requires a loading fixture large enough to test the entire aircraft wing. It is easy to understand that such an approach can be quite costly, time consuming and inefficient. It is therefore desirable to provide a method for measuring a strength of a test specimen at a localized region.
The above and other objectives are provided by a method for measuring a strength of a test specimen in accordance with the present invention. The method includes the steps of selecting a tensile load of interest for the test specimen, and bulk heating the test specimen at a localized region such that the test specimen is placed under the tensile load of interest. The method further provides for determining whether the tensile load of interest has caused a failure at the localized region. Bulk heating the test specimen provides a non-destructive evaluation (NDE) technique that is unachievable through conventional approaches.
Further in accordance with the present invention, a method for determining whether a tensile load of interest has caused a failure at a localized region of a test specimen. The method provides for observing a free surface of the test specimen with an optical interferometer. A measurement response of the free surface is determined with the optical interferometer, where the measurement response results from the tensile load of interest. The method further provides for determining whether the measurement response corresponds to a failure of the test specimen. In a highly preferred embodiment, surface velocity is selected as the measurement response.
In another aspect of the invention, a strength measurement system is provided. The strength measurement system includes a test cell, an electron accelerator, and a surface measurement system. The test cell contains a test specimen, and the electron accelerator applies electron beam irradiation to the test specimen. The electron beam irradiation bulk heats the test specimen at a localized region such that the test specimen is placed under a tensile load of interest. The surface measurement system determines whether the tensile load of interest has caused a failure at the localized region.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute part of this specification. The drawings illustrate various features and embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.